The pressure at which typical gas distribution systems supply gas may vary according to the demands placed on the system, the climate, the source of supply, and/or other factors. However, most end-user facilities equipped with gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with a predetermined pressure, and at or below a maximum capacity of a gas regulator. Therefore, gas regulators are implemented into these distribution systems to ensure that the delivered gas meets the requirements of the end-user facilities. Conventional gas regulators generally include a closed-loop control actuator for sensing and controlling the pressure of the delivered gas.
In addition to a closed loop control, some conventional gas regulators include a balanced trim to improve the reaction of the gas regulator to variations in the downstream pressure. The balanced trim is adapted to reduce the influence of the upstream pressure on the performance of the gas regulator. The upstream pressure is placed in fluid communication with a balancing diaphragm to apply a force to the control element of the gas regulator in the opposite direction as the force of the downstream pressure. Accordingly, as the upstream pressure varies, a corresponding force is applied to balance the force created by the upstream pressure as described further below so that the gas regulator acts in response to the downstream pressure only.
Some conventional gas regulators also include secondary devices, such as overpressure monitoring devices, slam shut devices, token alarms and the like, that perform a responsive action if a sensed input pressure, such as a pressure downstream of the regulator, varies from a predetermined normal operating pressure range. An overpressure monitoring device controls the pressure downstream of the regulator in the event that the regulator fails, thereby allowing the downstream pressure to increase to undesired levels. In the event the regulator fails and the downstream pressure rises above a predetermined monitor setpoint pressure, the overpressure monitoring device operates to close the valve port of the regulator valve and cut off the flow of gas to the downstream components of the gas distribution system. As demand increases and/or the problem with the regulator is resolved and the downstream pressure drops, the monitoring device opens the valve port and thereby allows gas flow downstream.
In other implementations, the gas regulators require safety devices to shut off the flow of gas if the regulator fails or other conditions develop that cause an overpressure or underpressure situation downstream of the gas regulator. Most commonly, slam shut safety valves are used to shut of the gas flow in one of these situations, or when either situation occurs. The slam shut safety valve may generally be disposed at or upstream of the regulator so that the slam shut valve may prevent gas from reaching the pressure reducing regulator in the event of the overpressure or underpressure conditions. The slam shut valve monitors gas pressure downstream of the gas regulator for maximum and minimum pressure tolerances. If the downstream pressure exceeds a maximum setpoint pressure or drops below a minimum setpoint pressure, the slam shut safety valve closes, cutting off the flow of gas to the gas regulator and preventing uncontrolled leak of gas. Once closed, the slam shut valve typically remains closed until service is performed and the slam shut valve is manually reset. In other implementations, it may be preferable to use a secondary device in the form of a token alarm device that does not relieve pressure in an overpressure situation, but instead bleeds an amount of the gas to produce an odor alerting the end customer to contact the gas provider for servicing of the gas regulator.
FIGS. 1 (closed position) and 2 (full open position) depict one conventional gas regulator 10. The regulator 10 generally comprises an actuator 12 and a regulator valve 14. The regulator valve 14 defines an inlet 16 for receiving gas from a gas distribution system, for example, and an outlet 18 for delivering gas to an end-user facility such as a factory, a restaurant, an apartment building, etc. having one or more appliances, for example. Additionally, the regulator valve 14 includes a valve port 20 disposed between the inlet 16 and the outlet 18. Gas must pass through the valve port 20 to travel between the inlet 16 and the outlet 18 of the regulator valve 14.
The actuator 12 is coupled to the regulator valve 14 to ensure that the pressure at the outlet 18 of the regulator valve 14, i.e., the outlet pressure, is in accordance with a desired outlet or control pressure, known as the setpoint pressure. The actuator 12 is therefore in fluid communication with the regulator valve 14 via a valve mouth 22 and an actuator mouth 24. The actuator 12 includes a control assembly 26 for sensing and regulating the outlet pressure of the regulator valve 14. Specifically, the control assembly 26 includes a diaphragm 28, a piston 30, and a control arm 32 having a valve disc 34 operatively connected thereto. The conventional balanced trim valve disc 34 includes a generally cylindrical body 36 and a sealing insert 38 fixed to the body 36. The control assembly 26 may also include a balanced trim assembly 40 with a balancing diaphragm 42 to offset the force applied to the valve disc 34 by the upstream pressure. The actuator diaphragm 28 senses the outlet pressure of the regulator valve 14 via a Pitot tube 44 placing the outlet 18 in fluid communication with the interior of the actuator 12 and a bottom-side of the actuator diaphragm 28. The control assembly 26 further includes a control spring 46 in engagement with a top-side of the diaphragm 28 to offset the sensed outlet pressure. Accordingly, the desired outlet pressure, which may also be referred to as the control pressure or the actuator setpoint pressure, is set by the selection of the control spring 46.
The diaphragm 28 is operably coupled to the control arm 32, and therefore, the valve disc 34 via the piston 30, controls the opening of the regulator valve 14 based on the sensed outlet pressure. For example, when an end user operates an appliance, such as a furnace, for example, that places a demand on the gas distribution system downstream of the regulator 10, the outlet flow increases, thereby decreasing the outlet pressure. Accordingly, the diaphragm 28 senses this decreased outlet pressure. This allows the control spring 46 to expand and move the piston 30 and the right-side of the control arm 32 downward, relative to the orientation of FIG. 1. This displacement of the control arm 32 moves the valve disc 34 away from the valve port 20 to open the regulator valve 14. FIG. 2 depicts the valve disc 34 in a normal, open operating position. So configured, the appliance may draw gas through the valve port 20 toward the outlet 18 of the regulator valve 14.
In the conventional regulator 10 depicted in FIGS. 1 and 2, the control assembly 26 further functions as a relief valve, as mentioned above. Specifically, the control assembly 26 also includes a relief spring 48 and a release valve 50. The diaphragm 28 includes an opening 52 through a central portion thereof and the piston 30 includes a sealing cup 54. The relief spring 48 is disposed between the piston 30 and the diaphragm 28 to bias the diaphragm 28 against the sealing cup 54 to close the opening 52, during normal operation. Upon the occurrence of a failure such as a break in the control arm 32, the control assembly 26 is no longer in direct control of the valve disc 34 and inlet flow will move the valve disc 34 to an extreme open position. This allows a maximum amount of gas to flow into the actuator 12. Thus, as the gas fills the actuator 12, pressure builds against the diaphragm 28 forcing the diaphragm 28 away from the sealing cup 54, thereby exposing the opening 52. The gas therefore flows through the opening 52 in the diaphragm 28 and toward the release valve 50. The release valve 50 includes a valve plug 56 and a release spring 58 biasing the valve plug 56 into a closed position. Upon the pressure within the actuator 12 and adjacent the release valve 50 reaching a predetermined threshold pressure, the valve plug 56 displaces upward against the bias of the release spring 58 and opens, thereby exhausting gas into the atmosphere and reducing the pressure in the regulator 10.
While the release valve 50 operates to vent gas from the actuator 12, it typically does not relieve sufficient pressure to maintain the downstream pressure below the upper limit for which the regulator 10 is designed to regulate. For such situations, a secondary device such as those discussed above may be provided to control and cut off the gas flow, or minimally to alert the customer that an overpressure situations exists. In the configuration illustrated in FIGS. 1 and 2, an overpressure monitoring device 60 operates to cut off the flow through the regulator valve body 14 until the downstream pressure is reduced after the failure of the regulator 10. In the illustrated example, the monitoring device 60 has a similar configuration as the actuator 12. The monitor 60 is coupled to the regulator valve 14 opposite the actuator 12 and on the upstream side of the valve port 20. The monitor 60 is therefore in fluid communication with the regulator valve 14 via an upstream valve mouth 62 and a monitor mouth 64 connected by a monitor housing 66. The monitor 60 includes a control assembly 68 for sensing the pressure downstream of the regulator valve 14 and closing the valve 14 when the downstream pressure exceeds a monitor setpoint or cutoff pressure. The control assembly 68 includes a diaphragm 70, a piston 72, and a control arm 74 having a valve disc 76 operatively connected thereto. The monitor 60 has balanced trim, and the valve disc 76 includes a generally cylindrical body 78 and a sealing insert 80 fixed to the body 78. The balanced trim includes a balancing diaphragm 82 to offset the force applied to the valve disc 76 by the upstream pressure.
The monitor diaphragm 70 senses the outlet pressure of the regulator valve 14 via an external downstream pressure feedback line 84 connected to a port 86 of the monitor housing 66. The feedback line 84 places a downstream point remote from the regulator valve 14 in fluid communication with the interior of the monitor 60 and a bottom-side of the monitor diaphragm 70. The control assembly 68 further includes a control spring 88 in engagement with a top-side of the diaphragm 70 to offset the sensed downstream pressure. The desired setpoint or cutoff pressure is set by the selection and compression of the control spring 88. The diaphragm 70 is operably coupled to the control arm 74 and, therefore, the valve disc 76 via the piston 72, and controls the closing of the regulator valve 14 in an overpressure situation. A balancing spring 90 biases the valve disc 76 toward the open position as shown, and the piston 72 and control arm 74 are coupled so that the control arm 74 is only driven when the diaphragm 70 senses a downstream pressure greater than the cutoff pressure and flexes (not shown) upwardly to drive the piston 72. The diaphragm 70 and piston 72 also react to pressure decreases, but the piston 72 does not drive the control arm 74 when the downstream pressure is less than the cutoff pressure. In the event of a failure of the monitor 60, the monitor 60 may include a release valve 90 similar to the release valve 50 of the actuator 12 to vent gas into the atmosphere.
The regulator 10 having an actuator 12 and an overpressure monitor 60 as described above has two primary functions. First, the regulator 10 transfers a volume of fluid downstream while maintaining a consistent outlet pressure. Second, the regulator 10 ceases to allow fluid flow to the downstream portion of the distribution system if the outlet pressure can no longer be maintained by the regulator 10. As to the first function, a key aspect of the performance of the regulator 10 is how much fluid volume can be maintained at a certain pressure. To optimize the fluid volume, it is preferable to sense the downstream pressure as shown in FIGS. 1 and 2 within the outlet 18. The Pitot tube 44 as positioned provides rapid feedback of the downstream pressure to the control assembly 26 and eliminates the need for an external downstream pressure feedback line. Presently, such internal sensing has not been widely applied for secondary devices such as the monitoring device 60.
Performance can be compromised when the actuator 12 and a secondary device use different sensing locations, but external sensing is still predominantly used for overpressure monitors, slam shut valves, token alarms and other secondary devices. External sensing for secondary devices presents various problems. For example, piping downstream lines requires additional maintenance and can be costly for gas companies having many regulators in the field. Additionally, exposed downstream lines, if damaged, make the secondary devices inoperable. If the secondary device cannot sense the downstream pressure, the secondary device cannot cut off the fluid flow or otherwise signal that a problem exists, thereby leading the operators to the incorrect assumption that the regulator 10 is operating properly. Therefore, a need exists for an improved regulator having internal pressure sensing for both the actuator and the secondary device.
Internal pressure sensing for a secondary device has been provided in regulator valves configured to condition the fluid flow for more accurate pressure sensing at the outlet 18. The flow conditioning quickly transitions the fluid from turbulent flow to laminar flow to provide for more accurate sensing of the downstream pressure. In one example of flow conditioning shown in FIG. 3, the regulator valve 14 of the regulator 10 has a modified outlet 92 configured to receive a flow control subassembly. The flow conditioning subassembly includes a screen 94 having a plurality of baffles or a mesh screen, a semicircular sieve 96 with a plurality of holes therethrough, and a central sensing tube 98. An inward end of the sensing tube 98 is placed in fluid communication with the interior of the actuator 12 and the interior of the monitor 60 via passages 100, 102, respectively, and the port 86 is capped to prevent leakage. The fluid flow is converted from turbulent flow to laminar flow as the fluid passes between the screen 94 and through the sieve 96, resulting in a more accurate measurement of the downstream pressure at the sense point of the sensing tube 98. While being effective at conditioning the flow, the flow conditioning subassembly is relatively expensive to fabricate. Moreover, the subassembly requires significant and costly modifications to the standard regulator valve body and is not readily transitioned to other body sizes. Therefore, a need exists for internal dual pressure sensing for an actuator and a secondary device in a gas regulator that is less expensive to implement and readily implemented in a variety of regulator valve sizes and body types.